Target: change member from reference to pointer

Target: change member from reference to pointer

This is a preliminary step to help ease the construction of CallLoweringInfo.
Changing the construction to a chained function pattern requires that the
parameter be nullable.  However, rather than copying the vector, save a pointer
rather than the reference to permit a late binding of the arguments.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209080 91177308-0d34-0410-b5e6-96231b3b80d8